Precision potentiometer



June 17, 1958 A. A. VERCESI 2,339,643

I PRECISION POTENTIOMETER Filed Sept. 17, 1956 3 Sheets-Sheet J INVENTOR A Mf/P/(O (4.1476655! Q ya-664401304 ATTORNEY A. A. VERCESI PRECISION POTENTIOMETER June 17, 1958 5 Sheets-Sheet 2 Filed Sept. 17, 1956 l N V E N TO R A f/fP/co A laecfs/ ATTO R N EY June 17, 1958 A. A. VERCESI PRECISION POTENTIOMETER 5 Sheets-Sheet 3 JNVENTOR. A/vse/co A. VfACfZS/ Filed Sept. 1'? 1956 BY j/w Gav/QM.

ATTORNEY United States Patent Oflice 2,839,643 Patented June 17, 1958 PRECISION POTENTIOMETER Americo A. Vercesi, Scarsdale, N. Y., assignor to Ford Instrument Co. Division of Sperry Rand Qorporation, Long Island City, N. Y., a corporation of Delaware Application September 17, 1956, Serial No. 610,301

4 Claims. (Cl. 201-56) This invention relates to infinite resolution potentiometers adapted to yield a linear or non-linear output at low noise and with minimum distortion.

Sliding contact potentiometers are generally provided with at least two brushes which are associated with the contact to make direct engagement with the resistance wire and with the slip ring for the contact. These separate brush engagements account for much of the noise in operation and the distortions in the output. The potentiometer embodying the invention contemplates the elimination of one source of noise and distortion by providing a rotatable and longitudinally slidable traveling contact having elements biased into continuous engagement with the resistance wire and an output conductor so that the function represented on the winding may be directly transferred from the wire to the conductor by means of the contact without the use of a slip ring and brush which frequently give rise to noise and distortion.

More particularly the invention provides means for cylindrically mounting an output sleeve about a stationary drum on which a resistance wire is disposed, there being interposed between the sleeve and drum a rotatable contact which threadably engages the insulated surface of the drum so as to be fed axially along the drum on rotation and is in continuous and permanent contact with the resistance wire and sleeve for low noise operation and infinite resolution.

One object of the invention is to provide a high precision potentiometer having infinite resolution.

Another object of the invention is to provide an infinite resolution potentiometer having coil contact means designed to eliminate noise characteristics due to manufacturing tolerances.

Other objects and advantages of the invention may be appreciated on reading the following description in conjunction with the accompanying drawings, in which Fig. 1 is an end view of the potentiometer;

Fig. 2 is an enlarged section taken on the line 2-2 of Fig. 1;

Fig. 3 is a partial section of the potentiometer;

Fig. 4 is a section taken on the line 44 of Fig. 3;

Fig. 5 is a section of the potentiometer showing an extreme adjusted position of the contact;

Fig. 6 is an enlarged section through one of the wire resistance carriers taken on the line 6--6 of Fig. 3;

Fig. 7 is an enlarged view of the sliding contact; and

Fig. 8 is an enlarged view of the traveling nut and one of the stops.

According to the drawings athreaded shaft 10 is journaled in bearings 11 and 12 in a cylindrical extension 13 of a frame 14 for the precision potentiometer. A knob 15 is mounted on one end of the shaft 10 extended through the frame 14. A panel 16 is screwed to the frame on the knob side thereof. An insulated disc 17 is secured to the other end of the shaft 10 within the housing provided by the frame 14 and cylindrical member 18 and end closure 19. A rotatable arm 21 is secured to the disc 17 by means of rivets.

A drum consisting of a plastic member 22 having threads with a coarse pitch is fitted to the cylindrical extension 13 of the frame 14 being secured thereto by pin 23 to prevent relative movement between the supporting and supported elements. A slidable contact 24 is slidably carried by the arm 21 being mounted to rotate concentrically about the member 22. A pair of guide cams 25 and 26 are integrally connected to the contact 24 and are adapted to straddle the coarse thread of the member 22 whereby linear movement of the contact 24 on the arm 21 is imparted by the rotation of the arm. The contact 24 has a depending finger 27 flexibly biased into engagement with a resistance coil 28 supported in shallow grooves cut into the face of the threads of the plastic member 22. The extreme ends of the resistance coil 28 is connected as by soldering to rivets 29 and 30 which are supported by the plastic member 22 at the two ends of the threaded convolutions. The inner ends of the rivets 29 and 30 receive the leads 31 and 32 of the input circuit. The lead 32 is passed through a longitudinal passage 33, in the plastic member 22 to provide for the completed circuit connection.

A stationary sleeve 34 to which the output of the potentiometer is directly transferred is mounted in the cylindrical member 18. The contact 24 is provided with a flexible pick-off finger 35 which is biased into continuous contact with the inner surface of the sleeve 34 to which is connected the output lead 36. The pressure engagement provided by the finger 35 on the sleeve is largely responsible for the low noise operation in the output side of the potentiometer. The leads 31, 32 and 36 are passed through an aperture 37 on the cylindrical member 18.

Stops 38 and 40 are pinned to the threaded shaft 10 near the respective ends of the extension 13 of the frame 14. The stops 38 and 40 are provided with axial extensions 38a and 40a to coact with similar extensions 42 and 43. A traveling nut 41 is carried by the shaft 10 intermediate stops 38 and 40. The traveling nut 41 is provided with extensions 42 and 43 adapted to engage face to face a corresponding extension on the stops at the established extreme positions of travel of the nut. The extensions 42 and 43 support key members 44 and 45, respectively, which ride in groove 46 in the extensions 13 of the frame, thus causing the nut to travel between the two stops on shaft rotation which is prevented when the stop nut contacts one of the stops and the contact 24 has reached a corresponding end of the resistance coil.

As shown the drum member 22 is cylindrical in shape which will cause the output of the device to be linear. Obviously, the drum may have some other contour when non-linear functions are desired. Other modifications in the invention may be made by persons skilled in the art without departing from the scope of the invention as defined in the appended claims.

What is claimed is:

l. A precision potentiometer comprising a stationary drum having a helical thread on its periphery, a resistance wire helically disposed upon the outer face of the helical thread, a stationary conductive sleeve concentrically surrounding the drum, an arm disposed within the space between the drum and sleeve and rotative concentrically about the drum, a pick-01f contact member slidably mounted on said arm and having a radial extension engaging in said helical thread, a flexible finger on the contact member resiliently bearing against the resistance wire, and a second flexible finger on the contact member resiliently bearing against the inner surface of the sleeve.

2. A precision potentiometer as defined in claim 1 in s which the inner surface of the sleeve is a smooth con- 4, A precision potentiometer as defined in claim 3 in tinuous surface. which the said arm is operatively attached to and elec- 3. A precision potentiometer as defined in claim 2 trically insulated from said shaft. together with a.manually: rotatable threader shaft axially bearing in the drum, limit stops at opposite ends of the :3 References Cited in the file of this patent thread portion of the shaft, and a nut on the said threaded portion between the stops non-rotatiyely engaging the UNITED STATES PATENTS drum. 2,712,584 Pantages July 5, 1955. 

